1. Field of the Invention
The present invention generally relates to an IC tag read-write apparatus and an antenna unit thereof, and more particularly to an IC tag read-write apparatus and an antenna unit thereof which have an increased flexibility in an installation location.
2. Discussion of the Background
A background IC (integrated circuit) tag read-write apparatus for reading and writing data relative to an IC tag installed in a remote apparatus has been widespread. One example IC tag read-write apparatus 100 is illustrated in FIG. 1. FIG. 1 illustrates the background IC tag read-write apparatus 100 and a plurality of IC tags TG1-TGn to which the background IC tag read-write apparatus 100 performs data read and write operations. In an alphanumeric expression of elements, such as TG1-TGn, n is an arbitrary integer greater than 1, such as 2, 3, 4, and so on and TG1-TGn means TG1, TG2, TG3, TG4, and TG5 when n is 5. This definition of n is applied to each case whenever it appears in an alphanumeric expression of elements described below.
As illustrated in FIG. 1, the background IC tag read-write apparatus 100 includes a transmission link 105, a circuit unit 106, a plurality of signal lines L1-Sn, and a plurality of antenna units ANU1-ANUn. The plurality of antenna units ANU1-ANUn have a structure similar to each other. That is, the antenna unit ANU1 includes a switch SWA1 and an antenna ANTA1, and the antenna unit ANUn includes a switch SWAn and an antenna ANTAn. In the plurality of antenna units ANU1-ANUn, an arbitrary antenna unit ANUk includes a switch SWAk and an antenna ANTAk. In an alphanumeric expression of elements, such as ANUk, k is an arbitrary integer varying from 1 to n.
In FIG. 1, the plurality of IC tags TG1-TGn have a structure similar to each other. That is, the IC tag TG1 includes an antenna ANTB1 and a modem DE1, and the IC tag TGn include an antennal ANTBn and a modem DEn.
The circuit unit 106 includes an oscillation circuit 101, a control circuit 102, and a modem 103. The control circuit 102 is connected to control gates of the switches SWA1-SWAn via the signal lines L1-Sn, respectively. Also, the modem 103 is connected to the switches SWA1-SWAn via the transmission link 105. In the circuit unit 106, the oscillation circuit 101 generates a carrier wave and sends it to the control circuit 102.
To perform a data writing to an arbitrary IC tag TGk, the control circuit 102 controls a data signal to be superimposed on the carrier wave output from the oscillation circuit 101, and exclusively turns on the switch SWAk of the antenna unit ANUk corresponding to the IC tag TGk. Upon receiving the carrier wave and the data signal from the control circuit 102, the modem 103 modulates the carrier wave in accordance with the data signal and sends the modulated data to the antenna ANTAk. The antenna ANTAk sends the modulated data by a radio wave. The IC tag TGk receives the radio wave sent from the IC tag read-write apparatus 100 with an antenna ANTBk and demodulates the received signal with a modem DEk.
To read data of the IC tag TGk, the IC tag read-write apparatus 100 initiates read command data to the IC tag TGk. Upon receiving the read command data, the IC tag TGk modulates the carrier wave based on requested data with the modem DEk and sends the modulated data by a radio wave with the antenna ANTBk. The IC tag read-write apparatus 100 receives the radio wave with the antenna ANTAk, demodulates the signal of the radio wave with the modem 103, and retrieves the data with the control circuit 102.
In the IC read-write apparatus 100 of FIG. 1, the cable length of the transmission link between the circuit unit 106 and each of the plurality of antenna units ANU1-ANUn is limited to the order of 200 mm due to an electric loss of the carrier wave which loss will be increased with an increase of a frequency of the carrier wave. This causes a great limitation to an arrangement of the circuit unit 106 and the plurality of antenna units AU1-AUn.